The following additional abbreviations are herewith defined:
3GThird Generation (cellular system)3GPPThird Generation Partnership ProjectBABCCH AllocationBCCHBroadcast Control ChannelBSICBase Station Identity CodeBSCBase Station ControllerBSSBase Station SystemBTSBase Transceiver StationCCCHCommon Control ChannelDSPDigital Signal ProcessorGSMGlobal System for Mobile CommunicationsIPInternet ProtocolMCUMicro-Control UnitMSMobile StationNCNetwork ControlPACCHPacket Associated Control ChannelPBCCHPacket Broadcast Control ChannelPSIPacket System InformationUMTSUniversal Mobile Telecommunications System
Reference can also be made, for example, to 3GPP TR 21.905, V4.4.0 (2001-10), Third Generation Partnership Project; Technical Specification Group Services and System Aspects; Vocabulary for 3GPP Specifications (Release 4).
When attached to a GPRS service, the MS can operate in one of the three NC modes, NC0, NC1 or NC2. The network controls the NC mode of the MS via information sent to the MS in broadcast or point-to-point messages.
In the NC0 mode the MS is responsible for selecting the best cell to camp on by performing CRS. In this mode the MS is not required to report the characteristics (received signal quality, etc.) of the surrounding cells to the network. In the NC2 mode the MS does not perform CRS independently, but instead it reports the characteristics of the surrounding cells to the network with a PACKET MEASUREMENT REPORT message. The network can, according to the measurement reports sent by the MS, command the MS to change cells. In the NC1 mode the MS performs both CRS and the measurement reporting.
In 3GPP Release 1999 (R99) the measurement reporting of surrounding 2G cells in the NC1 and NC2 modes is based on the GSM Neighbour Cell list. On the CCCH, the GSM Neighbour Cell list is constructed from the BA(list) (frequency list) broadcast in System Information 2/2bis/2ter messages, and from the BSIC list that is broadcast in the System Information Type 2quater message. However, if the BSIC list is not broadcast in the cell, the GSM Neighbour Cell list is defined to be equal to the BA(list) from the System Information Type 2/2bis/2ter messages. For GPRS neighbour cell measurement reporting, the BA(list) from the System Information Type 2/2bis/2ter messages is referred to as BA(GPRS).
When camping on a cell, the MS must acquire the GSM Neighbour Cell list from the system information before it can begin measurement reporting. The System Information 2quater message contains several message instances, and thus receiving the entire message takes some significant amount of time (up to tens of seconds, depending on the network configuration).
When the MS is moving rapidly the need to change cells occurs quite often, for example once every 15 seconds. However, when in the NC2 mode the network is unable to command the MS to change the cell until the MS has sent measurement reports, because without measurement reports the network does not know to which cell the MS should be assigned. Further, the MS must receive all instances of the System Information Type 2quater message before it is able to construct the GSM Neighbour Cell list. Thus, measurement reporting by the MS can begin only after the reception of the entire SI2quater message. However, the amount of time required to receive the SI2quater message is often so long that it is already too late to change the cell. As a result, the MS can drop out of service when moving outside the service area of the current cell. In practice, this situation is likely to occur, for example, on a highway in an area where the size of the cells is small.
The network could be configured not to use the System Information Type 2quater message, resulting in the GSM Neighbour Cell list being equal to the BA(GPRS) from the System Information Type 2/2bis/2ter messages, as described above. However, several procedures, e.g. GSM-UMTS interworking, require the presence of this message. Thus, eliminating the use of the System Information Type 2quater message is not an acceptable solution from a network configuration perspective.
Prior to this invention, there was no satisfactory solution to the problem described above.